Update: Tropical Storm Calvin now 720 miles east Big Island, forecast to reach Hawaiʻi by Tuesday night

Update at 11 a.m. July 17: Tropical Storm Calvin is now 790 miles east of Hilo and moving toward the Big Island at 21 mph with maximum sustained winds of 50 mph, according to the Central Pacific Hurricane Center.

Hurricane hunters are flying into the tropical storm to gather more information.

A Tropical Storm Watch remains in effect for the Big Island. It means tropical storm conditions are possible for the island within the next 36 to 48 hours.

On the forecast track, Calvin is expected to approach the main Hawaiian Islands on Tuesday, with tropical storm conditions possible over some areas of the Big Island starting Tuesday night.

Maximum sustained winds are near 50 mph with higher gusts. Calvin is forecast to gradually weaken during the next several days. The winds extend outward up to 125 miles from the center.

Rainfall: From Tuesday night into Thursday, storm total rainfall amounts of 4 to 8 inches are possible along windward areas of the Big Island, with lower amounts of 1 to 4 inches expected elsewhere in the state. This rainfall could lead to localized flash flooding and mudslides.

Surf: Swells generated by Calvin are expected to begin reaching the main Hawaiian Islands during the next couple of days. A rapid increase in surf is expected Tuesday and Wednesday. This surf will likely cause life-threatening surf along exposed east-facing shores.

For information from the Kauaʻi County about how to prepare and stay informed, click here.

Original post: A Tropical Storm Watch is in effect for the Big Island, and a Flood Watch was issued for both Maui County and Hawaiʻi Island, from Tuesday night through Wednesday afternoon.

Tropical Storm Calvin will produce periods of heavy rainfall over the Big Island all islands in Maui County that may lead to flooding conditions and landslides, especially along east and southeast facing slopes, according to the National Weather Service.

Primary impacts are expected on the Big Island, “where a period of heavy rainfall is expected, as well as high surf along east facing shores, and locally strong wind gusts.”

At 5 a.m., Calvin was located 920 miles east souteast of Hilo.

TIMING: Forecasters with the Central Pacific Hurricane Center say Calvin is expected to pass very close to the Big Island Tuesday night and early Wednesday, bringing a period of heavy rain, high surf and locally strong winds. The system is then forecast to weaken as it moves westward to the south of the other islands Wednesday and Wednesday night, brining the potential for some peripheral impacts, according to the CPHC forecast.

According to the latest National Weather Service forecast, “flooding rain will be possible as early as Tuesday evening on the Big Island, and chances for heavy rain is expected to increase for much of the state Tuesday night and Wednesday.”

WIND: The storm has maximum sustained winds of 50 mph with higher gusts and was moving toward the west near 18 mph, according to the Central Pacific Hurricane Center. The Central Pacific Hurricane Center reports that tropical-storm-force winds extend outward up to 105 miles from the center of the storm.

According to the National Weather Service: “Locally strong winds may begin as early as Tuesday evening across parts of the Big Island, with north winds shifting to the northeast and east as Calvin moves westward. Winds will primarily be northeasterly over the smaller islands, strongest Wednesday and Wednesday night.”

RAINFALL: The latest forecast calls for rainfall from Tuesday night into Thursday, with storm total rainfall amounts of 4-8 inches along windward areas of Hawaiʻi Island, and lower amounts of 1-4 inches elsewhere in the state.

SWELLS: On the water, swells generated by Calvin are expected to result in “rapidly building surf” along exposed windward coasts tomorrow night through Wednesday.  The National Weather Service reports that Surf Advisory levels are expected for most windward coasts, potentially reaching High Surf Warning levels (greater than 15 feet) along east facing shores of the Big Island.  The National Weather Service is forecasting peak surf on Hawaiʻi Island around low tide Wednesday morning.